Update optime/leader with checkpoint location after clean shut down (#1527)

Potentially this information could be used in order to make sure that there is no data loss on switchover.

patroni/dcs/__init__.py

@@ -758,10 +758,19 @@ class AbstractDCS(object):
         otherwise it should return `!False`"""
 
     @abc.abstractmethod
-    def delete_leader(self):
-        """Voluntarily remove leader key from DCS
+    def _delete_leader(self):
+        """Remove leader key from DCS.
         This method should remove leader key if current instance is the leader"""
 
+    def delete_leader(self, last_operation=None):
+        """Update optime/leader and voluntarily remove leader key from DCS.
+        This method should remove leader key if current instance is the leader.
+        :param last_operation: latest checkpoint location in bytes"""
+
+        if last_operation:
+            self.write_leader_optime(last_operation)
+        return self._delete_leader()
+
     @abc.abstractmethod
     def cancel_initialization(self):
         """ Removes the initialize key for a cluster """

patroni/dcs/consul.py

@@ -503,7 +503,7 @@ class Consul(AbstractDCS):
         return self._client.kv.put(self.history_path, value)
 
     @catch_consul_errors
-    def delete_leader(self):
+    def _delete_leader(self):
         cluster = self.cluster
         if cluster and isinstance(cluster.leader, Leader) and cluster.leader.name == self._name:
             return self._client.kv.delete(self.leader_path, cas=cluster.leader.index)

patroni/dcs/etcd.py

@@ -625,7 +625,7 @@ class Etcd(AbstractDCS):
         return self.retry(self._client.write, self.initialize_path, sysid, prevExist=(not create_new))
 
     @catch_etcd_errors
-    def delete_leader(self):
+    def _delete_leader(self):
         return self._client.delete(self.leader_path, prevValue=self._name)
 
     @catch_etcd_errors

patroni/dcs/kubernetes.py

@@ -546,9 +546,15 @@ class Kubernetes(AbstractDCS):
         resource_version = cluster.config.index if cluster and cluster.config and cluster.config.index else None
         return self.patch_or_create_config({self._INITIALIZE: sysid}, resource_version)
 
-    def delete_leader(self):
+    def _delete_leader(self):
+        """Unused"""
+
+    def delete_leader(self, last_operation=None):
         if self.cluster and isinstance(self.cluster.leader, Leader) and self.cluster.leader.name == self._name:
-            self.patch_or_create(self.leader_path, {self._LEADER: None}, self._leader_resource_version, True, False, [])
+            annotations = {self._LEADER: None}
+            if last_operation:
+                annotations[self._OPTIME] = last_operation
+            self.patch_or_create(self.leader_path, annotations, self._leader_resource_version, True, False, [])
             self.reset_cluster()
 
     def cancel_initialization(self):

patroni/dcs/zookeeper.py

@@ -315,7 +315,7 @@ class ZooKeeper(AbstractDCS):
     def _update_leader(self):
         return True
 
-    def delete_leader(self):
+    def _delete_leader(self):
         self._client.restart()
         return True
 

patroni/ha.py

@@ -748,13 +748,13 @@ class Ha(object):
 
         return self._is_healthiest_node(members.values())
 
-    def _delete_leader(self):
+    def _delete_leader(self, last_operation=None):
         self.set_is_leader(False)
-        self.dcs.delete_leader()
+        self.dcs.delete_leader(last_operation)
         self.dcs.reset_cluster()
 
-    def release_leader_key_voluntarily(self):
-        self._delete_leader()
+    def release_leader_key_voluntarily(self, last_operation=None):
+        self._delete_leader(last_operation)
         self.touch_member()
         logger.info("Leader key released")
 
@@ -784,8 +784,9 @@ class Ha(object):
         self.set_is_leader(False)
 
         if mode_control['release']:
+            checkpoint_location = self.state_handler.latest_checkpoint_location() if mode == 'graceful' else None
             with self._async_executor:
-                self.release_leader_key_voluntarily()
+                self.release_leader_key_voluntarily(checkpoint_location)
             time.sleep(2)  # Give a time to somebody to take the leader lock
         if mode_control['offline']:
             node_to_follow, leader = None, None
@@ -1384,7 +1385,8 @@ class Ha(object):
                                                                         stop_timeout=self.master_stop_timeout()))
             if not self.state_handler.is_running():
                 if self.has_lock():
-                    self.dcs.delete_leader()
+                    checkpoint_location = self.state_handler.latest_checkpoint_location()
+                    self.dcs.delete_leader(checkpoint_location)
                 self.touch_member()
             else:
                 # XXX: what about when Patroni is started as the wrong user that has access to the watchdog device

patroni/postgresql/__init__.py

@@ -13,7 +13,7 @@ from patroni.postgresql.bootstrap import Bootstrap
 from patroni.postgresql.cancellable import CancellableSubprocess
 from patroni.postgresql.config import ConfigHandler
 from patroni.postgresql.connection import Connection, get_connection_cursor
-from patroni.postgresql.misc import parse_history, postgres_major_version_to_int
+from patroni.postgresql.misc import parse_history, parse_lsn, postgres_major_version_to_int
 from patroni.postgresql.postmaster import PostmasterProcess
 from patroni.postgresql.slots import SlotsHandler
 from patroni.exceptions import PostgresConnectionException
@@ -310,6 +310,17 @@ class Postgresql(object):
         except (TypeError, ValueError):
             logger.exception('Failed to parse timeline from pg_controldata output')
 
+    def latest_checkpoint_location(self):
+        """Returns checkpoint location for the cleanly shut down primary"""
+
+        data = self.controldata()
+        lsn = data.get('Latest checkpoint location')
+        if data.get('Database cluster state') == 'shut down' and lsn:
+            try:
+                return str(parse_lsn(lsn))
+            except (IndexError, ValueError) as e:
+                logger.error('Exception when parsing lsn %s: %r', lsn, e)
+
     def is_running(self):
         """Returns PostmasterProcess if one is running on the data directory or None. If most recently seen process
         is running updates the cached process based on pid file."""

tests/test_ha.py

@@ -154,7 +154,10 @@ def run_async(self, func, args=()):
 @patch.object(Postgresql, '_cluster_info_state_get', Mock(return_value=3))
 @patch.object(Postgresql, 'call_nowait', Mock(return_value=True))
 @patch.object(Postgresql, 'data_directory_empty', Mock(return_value=False))
-@patch.object(Postgresql, 'controldata', Mock(return_value={'Database system identifier': SYSID}))
+@patch.object(Postgresql, 'controldata', Mock(return_value={
+    'Database system identifier': SYSID,
+    'Database cluster state': 'shut down',
+    'Latest checkpoint location': '0/12345678'}))
 @patch.object(SlotsHandler, 'sync_replication_slots', Mock())
 @patch.object(ConfigHandler, 'append_pg_hba', Mock())
 @patch.object(ConfigHandler, 'write_pgpass', Mock(return_value={}))

tests/test_kubernetes.py

@@ -113,7 +113,7 @@ class TestKubernetes(unittest.TestCase):
         self.k.initialize()
 
     def test_delete_leader(self):
-        self.k.delete_leader()
+        self.k.delete_leader(1)
 
     def test_cancel_initialization(self):
         self.k.cancel_initialization()

tests/test_postgresql.py

@@ -338,6 +338,11 @@ class TestPostgresql(BaseTestPostgresql):
         with patch.object(Postgresql, '_query', Mock(side_effect=RetryFailedError(''))):
             self.assertRaises(PostgresConnectionException, self.p.is_leader)
 
+    @patch.object(Postgresql, 'controldata',
+                  Mock(return_value={'Database cluster state': 'shut down', 'Latest checkpoint location': 'X/678'}))
+    def test_latest_checkpoint_location(self):
+        self.assertIsNone(self.p.latest_checkpoint_location())
+
     def test_reload(self):
         self.assertTrue(self.p.reload())